Every penetration in a fire-rated assembly has the potential to undermine compartmentalization if not properly treated, and plumbing services are among the most frequent and potentially vulnerable interruptions of floor and wall fire separations. Effective fire stopping of these penetrations is not a mere detail: it is a linchpin of occupant safety, risk management, and code compliance under Alberta’s adoption of the National Building Code of Canada (NBC).

The Function and Vulnerability of Fire Separations

Compartmentalizing a building through fire-rated floor and wall assemblies is the primary defense against rapid fire and smoke spread. Openings for mechanical, electrical, and particularly plumbing systems are inevitable, yet each creates a potential channel for fire and products of combustion. Large multifamily projects, as well as moderate-density residential sites in Alberta, present additional challenges due to the proliferation of stacked plumbing.

Effective compartmentalization requires that every penetration has a fire stopping solution with documented performance, ideally matched precisely to the assembly and service configuration. Failures routinely occur not from large openings but from incremental gaps around pipes, inconsistent materials, or poorly executed details at line intersections, chase terminations, and cross-discipline interfaces.

Key NBC Requirements: Article 9.10.16.1.(2) and Related Provisions

Under NBC 9.10.16.1.(2), horizontal concealed spaces-floor cavities, attics, ceiling voids, and crawl spaces-require fire stops to prevent lateral fire spread. The obligation is particularly acute at every interconnection between horizontal and vertical spaces, including intersections where plumbing penetrates both types of assemblies. If any exposed construction material within these spaces exhibits a surface flame-spread rating over 25 (such as most untreated lumber, some composite sheets, or plastic insulation), the need for robust fire stops is heightened.

Critical language in the code mandates continuous separation by fire stops, not simply at points of pipe passage but throughout the assembly at all interconnections and edges. The performance expectation is that fire and smoke must not find a path through or around penetrations during the fire separation’s rated period. This means more than incidental caulking or stuffing-it means purpose-selected materials installed to specified standards and thicknesses.

Prescribed Materials and Minimum Thicknesses for Fire Stops

Article 9.10.16.3 lists accepted materials and the specific minimum thicknesses required to be recognized as a fire stop. The NBC-approved materials reflect a spectrum of available building products, yet the code’s intent is to ensure that only durable, noncombustible, and dimensionally stable materials interrupt concealed spaces:

  • Sheet Steel: Requires a minimum thickness of 0.38 mm. Sheet steel is durable, noncombustible, and easy to fasten for large openings or chase closures. It resists warping and erosion under fire exposure and is readily available, but must be cut and sealed appropriately around service penetrations.
  • Asbestos Board: Historically listed at a minimum of 6 mm, but current practice in Alberta bans asbestos in new construction. For legacy assemblies, this provision remains relevant for evaluation and upgrades. Equivalent non-asbestos cementitious boards are used in modern applications, still honoring the 6 mm minimum for similar fire resistance.
  • Gypsum Wallboard: Requires a minimum of 12.7 mm. Standard Type X fire-rated gypsum board offers predictable fire resistance and is often the go-to for closing wall cavities, soffits, and chase ends. Proper fastening and complete coverage are crucial, with any joints lapped and taped as per fire separation assembly details.
  • Plywood, OSB, Waferboard: Minimum thickness of 12.5 mm, with a strict requirement for continuous supports at all joints. Only listed fire-resistive grades should be used, certain treated plywoods may have increased flame-spread or smoke development not suitable for fire stops.
  • Lumber: Either two staggered layers of 19 mm lumber (yielding 38 mm total), or a single piece of 38 mm lumber. This requirement emphasizes not just thickness, but the mass and overlap at joints-single layers are only compliant when continuous and tightly fit.

Selection among these materials is influenced by the expected fire exposure, occupancy type, penetrant size and configuration, and architectural intent. In areas of high service concentration, sheet steel and gypsum wallboard tend to be preferred for their combination of resilience and easy detailing; in wood-framed assemblies, plywood or lumber may dominate, so long as minimum thickness and support at all joints are honored.

The Gap Around the Pipe: Sealing the Opening with Fire Stop Systems

A hole cut for a plumbing pipe can easily exceed the pipe diameter by several millimeters to accommodate tolerances, pipe expansion, insulation, or fitting sweeps. The annular gap around each penetration represents a direct path for fire and smoke unless reliably sealed.

Where a fire stop of prescribed thickness is in place and subsequently penetrated, the NBC requires that the integrity of the fire stop be maintained. This obligation includes:

  • Continuous Fire Stopping: Filling all gaps between the penetration and the fire stop material-no air passage, no loose-fitting seals.
  • Listed Fire Stop Sealants and Collars: Only sealants, foams, pipe collars, or wraps listed for fire stopping through-penetrations are acceptable. Generic construction caulks, spray foams, and non-rated mastics or tape are not sufficient. Compatibility and adhesion with both the pipe (especially where pipes flex or expand) and the assembly are paramount.
  • Assembly Listing and Manufacturer Requirements: Each fire stop system is tested as part of a specific configuration under CAN/ULC-S115 and must be installed accordingly, including annular space limits, pipe size, and substrate type. Deviations void the rating; field engineering judgments require written rationale.

Field verification often reveals three practical risks: excessive annular spacing between pipe and assembly, omission or insufficient thickness of fire stop sealant, and use of materials that shrink, crack, or debond over time. The safest practice is to minimize the cut hole, maintain a control on maximum annular gap (generally under 25 mm unless otherwise listed), and apply a fire stop sealant to the precise thickness and coverage specified for the assembly.

Minimum Thickness: Not Just for Fire Stops, Also for Penetration Seals

Fire stop materials at the pipe interface are not always the same thickness as the base material sidings with the assembly. Many listed systems require a minimum bead or plug of sealant (frequently 10-20 mm), the use of backing rods to ensure proper shape factor, or the installation of intumescent collars with a band thickness rated for the particular pipe size and type. Where the NBC references fire stop “systems,” it imports the thickness and detailing requirements of the product listing, which may exceed the raw material minimums in 9.10.16.3.

For example, a 12.7 mm Type X gypsum fire stop with a 50 mm PVC pipe penetration typically demands an intumescent wrap or collar tested for that precise combination-most often installed with at least 12 mm of intumescent material at the slab or wall face, and sometimes a depth plug or fire-stopping foam backfill as mandated by the listing.

Vigilance regarding sealant and wrap thicknesses must match the careful compliance with the underlying fire stop sheet, plate, or framing thickness. All products must remain in place and fully adhered through the fire event and typical building movements: a too-thin bead or insufficiently encapsulated collar will fail during either.

Sealing Combustible Plumbing Penetrations: Risks and Requirements

Combustible pipes-including most polyvinyl chloride (PVC), cross-linked polyethylene (PEX), and acrylonitrile butadiene styrene (ABS) pipes-present a compounded risk at penetrations, as they may not only allow fire passage but also melt or burn away, creating a dramatically larger void. The NBC directly addresses this vulnerability in Article 9.10.9.7, requiring that any combustible plumbing penetration through a fire separation must utilize a tested firestop system with a fire-resistance (F) rating at least equal to the fire separation itself, established via CAN/ULC-S115 fire exposure testing.

Key points from NBC on this interaction include:

  • A fire-stopping system for combustible pipe must close the void created by pipe melt or burn-out during fire conditions. Most often, this is achieved with intumescent collars or wraps that expand to plug the opening as the pipe degrades under heat.
  • The F rating of the tested system must match or exceed the required rating of the separation-commonly 45, 60, or 90 minutes in Alberta residential construction. Standard caulking or mineral wool packing alone is insufficient for plastic pipe scenarios, unless part of a tested system.
  • An exception is permitted for pipes serving directly from a noncombustible water closet and passing through a concrete slab, provided the annular space is carefully fire stopped-here, the slab itself provides the baseline fire resistance, but proper sealing remains necessary to prevent smoke communication.
  • In fully sprinklered compartments on both sides of a fire separation, certain combustible penetrations are permitted with compliant fire stop sealing. This recognizes the risk-mitigating effect of early fire suppression but does not waive fire stopping obligations.

Where fire stop systems incorporate intumescent collars for combustible pipe, thickness is critical: under-testing or use of generic wraps will not expand sufficiently to plug the void during fire, while over-thickened collars can impede pipe expansion or violate listing configurations. Site conditions must match those of the tested assembly-pipe size, wall composition, and annular gap all affect the required intumescent mass, typically detailed in the manufacturer’s approval data and supported by ULC or cUL system numbers.

Best Practices in Fire Stopping Plumbing Penetrations: Detailed Guidance

Selection of Systems and Materials

Only proprietary fire stop systems tested for the specific pipe type, assembly thickness, and configuration should be considered. Industry staples such as Hilti, 3M, STI, and Tremco all provide tested systems for typical ABS, PVC, PEX, and copper pipes passing through gypsum, lumber, or concrete separations. System selection should begin at project design-field substitutions or “or equal” substitutions must be backed by confirmed system listings and equivalency reports.

Pre-planning Pipe Layouts

Coordination between mechanical and architectural design can minimize unnecessary penetrations and foster grouping services into single, planned chase locations. Every added penetration is a new liability: limiting their number and ensuring adequate clearance for tested fire stop systems (especially where collars or thick wraps are needed) saves corrective effort and cost.

Precision in Hole Cutting and Preparation

Keeping holes tight around pipes limits the annular gap and makes sealing more effective. Over-drilling or “wallering out” holes to ease installation or fix misalignment becomes a frequent point of inspection. Maximum annular space permitted is system-specific-common listings allow 0-25 mm, but site practice should aim for the lower end. Where gaps exceed the tested listing, field engineering judgments or additional fire-stopping measures must be documented and validated through a design professional or manufacturer engineer.

Installation by Qualified Trades with Oversight

Installation of fire stop products is seldom a “by eye” process. Pipe collars must be correctly sized, wrap orientation must follow the tested protocol, and sealant depth and width must exactly match listing diagrams-too little is non-compliant, too much can push a system out of its listing’s tested parameters. Alignment, spacing to edges and other penetrants, and adherence to substrate are all critical. Superintendents should employ mock-ups, pre-pour or pre-board walkthroughs, and photographic documentation to enforce uniform standards.

Adherence to Manufacturer Instructions and Approvals

Each proprietary system manufacturer supplies both Written Installation Instructions (WIIs) and listing sheets referencing the tested assemblies. Cross-checking the project’s assembly conditions (wall/floor construction, piping material, hole size), system limitations, required backing or accessory materials, and allowable sealant or collar thickness is mandatory. Installation without reference to the detailed listing is a frequent point of deficiency found in warranty and regulatory review.

Inspection, Quality Control, and Recordkeeping

Ongoing site review, including third-party inspection in larger builds, ensures long-term performance and regulatory defensibility. Inspections should confirm:

  • That the fire stop material and system used are as specified and reflect the manufacturer’s tested assembly for the actual penetration configuration.
  • Minimum thickness of the fire stop sheet, board, or lumber matches code requirements.
  • Sealants/collars/wraps are installed to the depth and width specified by the system, with approved adhesion and in-service stability.
  • Penetrations do not introduce mechanical stress or displacement to fire stop materials over time.

Records should include make, model, and batch of fire stop products, installer/inspector names, photos of pre-close-in condition, and system reference numbers.

Maintenance and Refurbishment

Though fire stops are often presumed to remain undisturbed for the life of the building, renovations, repairs, or retrofits can breach previously sealed penetrations. Best practice incorporates tagged or mapped assemblies, maintenance manuals for facilities teams, and a clear protocol for re-sealing when penetrations must be reopened. This avoids legacy non-compliance and ensures continued fire separation integrity throughout building life cycles.

Common Pitfalls and Remedies

Gaping/Irregular Holes

Inconsistent or oversize holes-often the result of field corrections or misaligned coring-are a leading cause of failed fire separation integrity. Address through pre-installation coordination, use of hole-saw guides, and, where necessary, fire-rated escutcheon plates or non-shrink grout fillers before application of a listed fire stop system.

Improper or Unlisted Sealants

Using caulks, foams, or sealants without a tested fire rating for through-penetrations is a recurrent error, particularly with combustible pipes. These products may char or melt without expanding to seal the void, offering little fire protection. Always check fire stop system listings and submittals for the exact sealant, wrap, or collar required; off-label substitutions are not code-compliant.

Insufficient Thickness or Voids in Fire Stop Application

Even where the base fire stop material is sufficient, application of insufficient layers or incomplete coverage of sealant, missing wraps inside the hole, or poor lap jointing at multi-layer assemblies allow fire and smoke passage. Inspection and documentation-including probing behind exposed faces and borescope inspections for concealed cavities-are critical for full compliance.

Incompatible Assemblies and System Listings

The system listed for a steel pipe through concrete is almost never suitable for a plastic pipe through a wood-framed floor. Rely on third-party listing data (ULC, cUL, or manufacturer system numbers) for every unique interaction of pipe, assembly, and fire rating-and add field documentation to prove compliance.

Advanced Compliance Strategies for Alberta Multifamily Construction

The realities of the Alberta residential construction market, including often extreme cold-weather conditions, fast-and-tight construction schedules, and growing mechanical complexity, make the correct detailing and installation of fire stops around plumbing penetrations both challenging and critical. Advanced project teams foster compliance and durability through:

  • Preconstruction Coordination Meetings: Bringing drywall, mechanical, and fire stop installers together at design stage to review all planned penetrations and needed clearances, materials, and detailing-eliminating improvisation in the field.
  • Use of Mock-ups and Sample Walls/Floors: Building representative section mock-ups with installed services and full fire stop assemblies to test installation fit and finish, and to train trades on compliant practice.
  • Digital Coordination and Penetration Tracking: Employing BIM or other coordination tools to anticipate clashes, group penetrations, and select systems with known compatibility before site execution. Tracking each penetration from rough-in through close-in with photographic and GPS/location data strengthens post-occupancy defensibility.
  • 3rd-Party Inspection and Post-Installation Testing: Inviting experienced inspectors to verify fire stop integrity before drywall or slab closure prevents both costly remediation and failed occupancy inspections. For especially vulnerable assemblies, on-site fire resistivity spot testing (where permitted by code) yields added assurance.
  • Ongoing Education on Evolving Products and Test Standards: Manufacturers regularly introduce new fire stop solutions-ongoing education ensures site staff and installers use current, compliant products and installation methods. Subscription to manufacturer technical bulletins and code update seminars is recommended.

Summary Chart: NBC-Approved Fire Stop Materials and Minimum Thicknesses

  • Sheet Steel: 0.38 mm minimum
  • Asbestos Board (legacy only): 6 mm minimum
  • Type X Gypsum Wallboard: 12.7 mm minimum
  • Plywood, OSB, Waferboard: 12.5 mm minimum (with continuous, supported joints)
  • Lumber: 2 x 19 mm (joints staggered), or 38 mm single layer

Best-Practice Action Plan to Maintain Fire Separation Through Plumbing Penetrations

  • Select tested and listed fire stop systems for each unique pipe material and assembly configuration, ensuring both base and sealant/wrap/collar thicknesses meet or exceed code and system requirements.
  • Plan penetrations during preconstruction to minimize quantity, group where feasible, and anticipate installation space for prescribed collars and wraps.
  • Drill or core holes tightly to pipe diameter to minimize annular gaps and simplify sealing.
  • Install fire stop sealants, wraps, or collars precisely to tested thickness and layout, following each system’s official listing or evaluation report.
  • Inspect regularly before assemblies are closed in; document every penetration with photos, system listing numbers, material batch/lot data, and installer sign-off.
  • Implement a maintenance protocol and tagging/database system so penetrations can be re-sealed immediately if disturbed during subsequent building lifecycle events.

Conclusion: Protecting Fire Compartments Through Informed Detail and Diligence

Preserving the integrity of fire separations in Alberta’s residential buildings depends upon strict adherence to the minimum thickness requirements and installation best practices for fire stopping at plumbing penetrations. The National Building Code explicitly defines minimum materials and thicknesses for base fire stops, and further demands listed, tested systems for sealing around all penetrations-especially where combustible pipes are present, given their greater vulnerability and potential to expand openings during fire.

Durable compliance is achieved not just by “checking the box” on material thickness but through proactive pre-planning, meticulous installation, and thorough documentation. The increasing complexity of modern multifamily projects in Alberta demands sophisticated coordination between all disciplines to deliver fire-resistive assemblies that meet both intent and letter of the code, from slab to ceiling and chase to suite. Recognizing that every plumbing pipe is a potential weak link-and that robust, code-conforming fire stops are the first line of defense-ensures both safety and asset value are protected across the lifecycle of the building.

Kingsway Builders consistently executes best-in-class fire stopping details on Alberta multifamily projects, delivering projects that exceed industry standards for safety and code compliance.